Defending champion Bill Haas outplayed the rest of the pack, firing an impressive seven-under 64, three shots better than the next lowest round — which is the second-largest margin of the season (Phil Mickelson was four clear of the rest when his putt for 59 lipped out in the first round in Phoenix).

Haas kicked off the day in a ho-hum style, parring the first hole, which is playing the easiest this week, at Riviera. He opened with four straight pars before he appeared to get his rhythm going with birdies on Nos. 5 and 7. But the game-changer was rolling in a tough 30-footer for birdie on No. 9, chipping-in for eagle on No. 10 and getting up-and-down (for birdie) on No. 11, and then he made some good par saves to keep the momentum going.

“No. 12 — that hole has kind of got my number so far,” said Haas, who has a three-shot lead over Webb Simpson, Charl Schwartzel and John Merrick heading into Sunday. “I think that’s going to be a key hole tomorrow, just if I can find that fairway, it will feel like a totally different hole, because I haven’t seen it yet.”

That’s an intimidating tee shot. Haas has still managed to par the hole in the first three rounds.

“I was kind of just plugging along,” said Haas, who is looking to become the first player to defend his title since Steve Stricker at the 2011 John Deere Classic. “Great save, great up-and-down at 17. I certainly would have liked to make that putt on 18 after a nice drive and a nice second shot, but overall, very pleased.”

Simpson was impressed with Haas’ round in conditions that reminded him of the brutally tough USGA setups.

“The course, as Bill just talked about, completely different from the first two days,” said Simpson, who exchanged a handshake/bro-five with Haas as they passed each other in the interview room. “It was firm and fast, and the back nine, especially, reminded me of a U.S. Open, just the way the ball is releasing, and the temperature got up, which made the ball go even further.

“So it was difficult to get the ball close to the pin, especially front pins. I had a lot of 3- and 4-footers today for par. Just managed myself well around the course, made one bogey. Bill shooting 7-under is incredible out there. I mean, it was very tough. I felt like my 3-under was pretty good. And I didn’t know what (Bill) shot. I just looked at my phone as I was waiting.”

While it’s difficult to go low at Riviera, it’s also easy to blow up and make doubles, as most in the field will tell you. However, Haas hasn’t even made a bogey in the last 40 holes.

“Just try not to get ahead of it,” said Haas, referring to a swing thought that has helped him. “That’s kind of my biggest flaw is I don’t turn and I kind of get ahead of it. You’ll see it a few times, hopefully not tomorrow, but I hit some right shots and just really trying to work on, I don’t even know how you want to say it, but hitting it high.

“On the range, I try to hit a lot of shots high, like pretend there’s a tree in front of me, which if you’re hitting a shot high, you can’t get in front of it. It helps you stay behind the ball a little bit. It’s kind a simple swing key but that’s what I’m working on.”

Haas is ranked first in ballstriking this week, but he’s also rolling it well on the greens — he only needed 24 putts on the way to his 64 on Saturday.

He made a change at the Waste Management Phoenix Open, lengthening his Scotty Cameron putter by an inch.

“It’s something I think feels a little more comfortable,” said Haas after the second round in Scottsdale, where he went on to finish T6. “This has been the first week where I feel like I’m rolling it nice for two days, and I don’t know if that’s exactly the key, but it was a little bit.

“I was talking about Stan Utley and he basically said, who says what standard is. We’re all different. You shouldn’t use a 35-inch putter because you’re shorter than me. You should use a shorter one. So my standard maybe is a little longer.”

Haas is using a conventional stroke rather than the belly putter that was in his bag during last year’s victory. He asked Stan Utley to take a look at him (officially) for the first time the week of the Phoenix Open.

Haas will try to continue his superb ballstriking and putting on Sunday, which will crucial to hold on for the win. (Well, I think if he shoots even-par or one-under, he’ll be fine.)

“To have success out here, you’ve got to putt well, and yesterday I chipped in on the last hole for par. I certainly was not playing that well, and to be able to shoot 4-under you can say I’m playing well but if you watched me play yesterday, you wouldn’t have said that.

“Today I struck the ball a little bit better and the putter felt pretty good. No one thing; every day is a new day and you’re always working. My dad always said, when you’re playing well, you’re not far off from playing poorly; and when you’re playing poorly, you’re not far off from playing well. So there’s just such a fine detail in your swing that can change daily. So you just always keep working on it.”